"I just think they would probably laugh at me. I only need 1 tube...."
Nahh, Wolverine tube is a very professional company. I dealt with a young lady, she worked up a quote and actually called me back when she said she would. (very unusual) I placed the order and they cut the flues, cleaned and chamfered the ends and even gave me one extra tube. I no longer have that available as it is the liner for my 103 caliber black powder rail gun. No steamboat is complete without one.
I don't really think you're going to see anything conclusive by a slight change in one family of alloys. One has a range of products of high iron content, and the other predominantly of copper.
"unless you have test apparatus that can reliably recognize a difference in performance with four significant figures, and can maintain a test with applied conditions equally precise, then your test results would range from "highly unreliable" to "useless""
Which "four significant figures" are being referenced? I don't think the test I ran and they way it was ran was by any means perfect (is there such a thing?), but I don't think it was highly unreliable or useless. Everything was at same ambient temperature to begin, very close to the same amount of water in each. Same torch setting for both and the time was monitored very close. Perfect test? No, However, I do believe it showed that wall material type is not very important and there is no vast difference between steel and copper.
I could run a much better test, but I'm not going to invest the money in equipment needed, it simply isn't that important to me and would probably still only result in some similar outcome. It served to quell the suspicion I had.
As I eluded to above, many more qualified folks have obviously ran similar tests over the years with much better equipment and obviously arrived at a similar result as my rudimentary test. If there was a proven scientific opinion that copper was better than steel for heat transfer, it would not only be a good idea to use it, there would probably be Federal EPA mandates stipulating it's use where applicable.